Tuesday, April 23, 2013

Finally, a swallow that nests only where it is supposed to.
Bank Swallows (Riparia riparia) nest
in sand banks, usually in colonies, sometimes in very large colonies. These vertical
or near-vertical banks are typically along rivers but may be in dry areas as
well, even sand quarries and piles of sand thrown up by construction and then
abandoned. Thus like all other swallows, their nest sites can be augmented by
human activities.

Bank Swallows are common breeding birds across northern
North America. They winter mostly in South America and are common migrants in
between. Breeding also all across Eurasia, they are one of the most widely
distributed songbirds (like the Barn Swallow).

Bank Swallow colonies range from just a few birds to up to
1,500 active nests. The burrows can be quite near to one another but stretch
for hundreds of feet along a bank.

At new sites, males begin excavating burrows as pairs are
forming. A male with a burrow will fly after a female and attempt to attract
her to the burrow, where he lands at the opening. If she is interested, she
will accompany him inside, where copulation takes place.

Although Bank Swallows are socially monogamous, males
constantly attempt extra-pair copulations. When a female leaves the nest, her
mate often flies right on her tail to keep other males from attempted mating,
and this is successful most of the time. These flights, usually with three or
more birds, can be seen constantly around colonies early in the season. One
researcher found that males could actually distinguish heavier females,
apparently receptive to breeding, and preferentially chase them.

The burrow is dug with beak, feet and wings. The excavation
takes about 4 or 5 days, and then the female begins to gather material for the
nest at the end of the burrow, taking another few days. The four or five eggs
are laid one each day, and incubation, mostly by the female, ensues for about
two weeks after the last egg is laid.

Both adults gather food for the brood, and it has been
estimated they bring about 60 prey items/visit and feed the entire brood about
7,000 insects in total. If you're worried about bugs, it would seem to pay to
live near a Bank Swallow colony. 500 nests x 7,000 insects = 3.5 million fewer
insects in three weeks! But what would the Society for the Prevention of
Cruelty to Insects say about that?

The young leave the nest at about three weeks of age and
gather in communal perching areas, where they are fed for up to another week.
Adults recognize their own young vocally among the clamoring of many
individuals, much like the case in a tern or gull or penguin colony.

Tuesday, April 9, 2013

I recently learned of a Great Blue Heron nesting colony in
Kenmore, Washington, only 10 minutes from my house. But the colony, at the edge
of a park and ride lot, was at some distance from the vantage point, so it
would take a long telephoto to get good photos of them. So I went up there with
my new Canon PowerShot SX50 HS camera with its 50x zoom lens.

The colony has about 50 obvious nests, although not that
many pairs were present during my two morning visits. Activity levels were low,
consisting mostly of birds flying out to gather additional nesting material.
But that activity had birds flying in with twigs and branches often enough to
be photogenic, and a few birds even landed in the nearby Douglas-firs to tug on
live branches. Otherwise the herons stood quietly at their nests.

The nests are reused for many years, birds sometimes
changing nests between years. I don't know what happens when a bird chooses a
nest and its previous owner returns soon thereafter! You do see sparring in the
colonies.

Males procure the nest material and females remain at the
nest to put it in place, and I saw numerous such exchanges. The sexes can't be
distinguished, so all one can do is make assumptions that are supported by
previous research. The first eggs should be laid in March, according to the
literature, so presumably in early April some of the birds had clutches
already. Indeed, some birds were flat on the nest, presumably incubating.

Copulation takes place both before and during egg laying, and one such act was
observed during a two-hour visit. Both sexes incubate, alternating during the
24-hour period (females more at night), and the total incubation period is
about 27 days. Hatching is asynchonous, as incubation begins when the first egg
is laid, so the youngest bird may be several days younger than the oldest.

Once the eggs hatch, the young remain in the nest 7-8 weeks,
so there will be plenty of photo opportunities to come. One thing I will be
looking for is siblicide, where a young bird attacks and actually kills a
nestmate. The prey is often dropped into the nest in the midst of the young,
and especially when the items are small, the young are more likely to fight
over them. When food is limited, it makes evolutionary sense for the brood to
be reduced, so the remaining young will have sufficient food to grow and
fledge.

Great Blue Herons have had a hard time of it in the Seattle
area, as Bald Eagles, which have increased tremendously in recent years, visit
their colonies as they are forming and take eggs, young or adults if they can
catch them. A few such disturbances will usually cause the adults to desert the
colony. They can either move elsewhere or just fail to breed. The next season
they try again at another spot, and there is a fair likelihood that eagles will
find that spot as well.

I keep hoping that the eagles won't destroy this colony. It
has been established for a decade at least, so there is hope. On occasion,
herons nest very near an eagle nest, and apparently that keeps other eagles
away from the heron colony. I don't know why the resident eagle doesn't take
its toll.

Tuesday, April 2, 2013

Just as Cliff Swallows adjusted to the push of humans (and
their structures) across North America, so did Barn Swallows (Hirundo rustica). This species,
virtually worldwide in distribution, has been known to be associated with
humans for over 2,000 years in Europe. But it may have had a limited breeding
range in North America, thought to be primarily in the mouths of caves.
Needless to say, these were very limited nesting habitats.

Nowadays, however, Barn Swallows nest throughout southern
Canada and the United States, excepting the southwestern deserts and peninsular
Florida. They are so successful because they nest on just about any structure
provided by humans—houses, barns, overpasses, bridges, even small culverts.
Drive across country, and there will be Barn Swallows nesting under just about
every bridge you cross. But look for them in vain on natural substrates!

Like Cliff Swallows, Barn Swallows utilize mud for the
foundation of their nest, and they gather it in the same way from the water's
edge, although singly rather than in groups. The mud walls are usually about an
inch thick. Rather than retort-shaped, their nest is cup-shaped, so the young
spend their time looking out at a broader world, although still constricted by
the ceiling of their nest site.

Some people think having Barn Swallows nest on their house
brings good luck. Others are turned off by the mess they make. The parents
collect fecal sacs from the nest for the first 12 days after the eggs hatch,
but after that the young just stick their rear end over the edge and let fly.
That's a lot of incremental excrement in the subsequent 8 days before they
fledge.

With clutch sizes averaging around five eggs, the nest of a
Barn Swallow fills up fairly rapidly with growing young, so the young need to
leave the nest as soon as they can fly. The adults "park" them on
nearby tree branches or fence wires and feed them for up to a week more. Then
they are on their own.

Barn Swallows have been much studied in Europe, especially
their mating behavior and sexual selection. Birds of both sexes with longer and
more symmetrical tails have greater reproductive success, parental effort, annual
survival, ability to withstand parasites, immunocompetence, and other measures
of fitness. Thus an individual has a fairly good chance of judging the true
quality of a prospective mate.

So Barn Swallows nested in caves, and Cliff Swallows nest on
barns. Care to guess where Cave Swallows nest?

Follow by Email

About the Slater Museum

Our goals are to preserve and provide a collection of specimens to be used for research and education. Located in Tacoma, Washington, the Slater Museum is one of the region's significant repositories for bird, mammal, reptile, amphibian and plant specimens from the Pacific Northwest. In addition, we strive to educate the local community about nature and about the value of museums.